This application claims convention priority from Japanese patent application No. 214736/96, filed on Aug. 14, 1996, the disclosure of which is incorporated herein by reference.
This invention relates to a gas detection method using a gas detector for detecting at least one of a halogen gas, a hydrogen halide gas, an acidic gas, an oxidizing gas, a basic gas and an organic acid gas from a mixed gas containing it, and to a detection apparatus for determining the concentration of the gas.
Various methods for detecting a harmful gas in a mixed gas such as air have hitherto been proposed. It is relatively more difficult to detect a component gas in a mixed gas than to detect a component in a liquid, particularly with high accuracy over a wide gas concentration range.
There has been a strong demand for methods for rapidly and easily detecting a harmful component in a mixed gas such as air with high accuracy over a wide concentration range, particularly methods for rapidly and easily detecting a harmful component in an exhaust gas discharged from semiconductor production plants or the like, such as a halogen or a hydrogen halide with good accuracy over a wide gas concentration range.
Recently, the inventors have found that tetraphenylporphyrin and tetraphenylporphyrin derivatives or metal complexes thereof are gas reactive pigments capable of reacting with a halogen gas, a hydrogen halide gas, an acidic gas, an oxidizing gas, a basic gas or an organic acid gas (hereinafter sometimes simply referred to as a halogen gas, a hydrogen halide gas or the like). Thus, an attempt was made to provide a method for determining the concentration of a halogen gas, a hydrogen halide gas or the like using such a gas reactive pigment based on a linear calibration curve drawn from the relation between the concentration of the gas and a color spectrum change in the gas reactive pigment in contact with the gas. (J. Mater. Chem., 1996, 6(6)953-956)
However, it was found to be difficult to draw a calibration curve with sufficiently high accuracy over a wide gas concentration range to determine the concentration of a gas such as a halogen gas, a hydrogen halide gas or the like from a change in the height of peaks of the color spectrum of a pigment, e.g., tetraphenylporphyrin in contact with said gas. This is because the height of spectrum peaks increasing with an increase in gas concentration reaches a plateau while the peaks are still low, and the calibration curve provides a linearity between gas concentration and the spectrum height over a limited range. Thus, a calibration curve prepared between the concentration of a gas of interest and the height of color spectrum peaks is not useful for determining the concentration of the gas to be measured because the calibration curve covers only a limited range.
To avoid the above problem, the concentration of a gas of interest such as a halogen gas, a hydrogen halide gas or the like had to be diluted or concentrated to adjust it to a level to which a calibration curve could be applied. However, it was difficult to precisely adjust the concentration of a gas, still more difficult to include such a process of adjustment in a continuous measurement for gas concentration.
In order to broaden the gas concentration range measurable in a method for determining the concentration of a gas such as a halogen gas using a gas detector comprising a gas reactive pigment, the inventors also made an attempt to use a plurality of gas detectors comprising different amounts of a gas reactive pigment therein. (J. Mater. Chem., 1996, 6(6)953-956; and U.S. Ser. No. 08/728,529, the disclosure of which is incorporated herein by reference) However, the use of a plurality of gas detectors in the attempt was inconvenient.